Numerous pipe inspection pigs are in existence and have been used in connection with non-destructive inspection of pipelines for gaseous or liquid materials, such as natural gas, liquid hydrocarbons, or water.
Various methods of detecting flaws or defects from the inside of a pipe or pipeline have been attempted with varying degrees of success. Ferromagnetic induction devices have been used as disclosed in U.S. Pat. No. 4,742,298. This invention was directed to determining the presence and the magnitude of surface flaws and to overcoming difficulties encountered in determining the presence and the magnitude of surface flaws in a pipe. The solution proposed was to use a cylindrical primary alternating current coil which is coaxially aligned with the pipe to generate a high frequency AC magnetic field in the pipeline, a multiple cylindrical secondary AC sensing coil where arranged at prescribed intervals in a circumferential direction around the interior of the pipe, each secondary coil having an axis parallel to the axis of the primary coil. The AC voltage sensed at each secondary coil is set to be proportional to the density of a parallel component of magnetic flux caused by the AC magnetic field generator.
Eddy current sensing probes have also been used primarily in connection with non-destructive inspection and testing of relatively thin-walled tubing which is not ferromagnetic material. Such tubing does exist in steam generators and heating exchangers having been the primary focus of eddy current probes as disclosed in U.S. Pat. No. 4,851,773 which discloses a single direction rotating head profilometer. One embodiment of that device discloses an electromechanical eddy current probe having a rotatable sensing head for sensing the wall thickness and for locating local defects in a tube or conduit through which it is passed. Basically, the mechanical profilometer probe was designed to detect dents in the interior surface of steam generator tubes. The position of the rotating head is varied along the length of the tubing being inspected as the probe is drawn through the tubing with a cable.
Another eddy current probe is disclosed in U.S. Pat. No. 4,952,875 in which a plurality of pairs of diametrically opposed sensing coils are altematingly staggered along the longitudinal axis of the test sensor to give complete coverage of the interior pipe surface and are further permitted to move in and out to accommodate the size differences or constrictions in the pipeline. However, the sensor probe is intended to move longitudinally through the pipeline.
Also, U.S. Pat. No. 5,068,608 discloses multiple coil eddy current probe system and an eddy current probe is disclosed in which a defect is first detected when the probe is positioned adjacent the defect and a series of axially spaced probes are activated to sense and detect the extremities of a crack or other discontinuity. Generally, eddy current probes have not been particularly successful with respect to underground pipelines constructed of steel or other ferromagnetic materials and having pipeline walls with thicknesses substantially greater than the normal eddy current penetration depth. However, one attempt to provide an eddy current probe or ferromagnetic pipeline flaw detection was disclosed in U.S. Pat. No. 4,107,605.
The most popular and currently most useful sensors for ferromagnetic pipeline inspection have been magnetic flux generators and magnetic flux leakage sensors which are positioned circumferentially around an inspection pig which is moved longitudinally through the pipeline. Examples of such sensors are disclosed in U.S. Pat. Nos. 4,105,972, 4,310,796, 4,444,777 and 4,458,601. The operation of such magnetic flux detection probes is described in U.S. Pat. No. 4,789,827 in connection with a magnetic flux detection probe in which the sensors are intentionally spaced at different radial distances or spaced at different distances from the interior pipe surface in an effort to obtain greater accuracy with respect to the location of the flaw or defect on the inside or the outside of the pipe wall.
Some attempts have been made to detect defects at different angular orientations in connection with testing and inspecting pipes as they are being manufactured. U.S. Pat. No. 3,906,357 discloses an exterior pipe testing device in which there are two external sensor sections, one having a plurality of fixed sensing shoes circumferentially spaced around the pipe to be inspected which depends upon linear movement of the pipe therethrough for detecting flaws or defects primarily oriented circumferentially around the pipe. A second inspection unit is provided which has a pair of opposed magnetic sensing shoes which is rotated rapidly around the outside of the pipe to be inspected in an effort to detect longitudinal cracks which might otherwise go unnoticed with the fixed shoe sensing unit. Complex circuitry is used to coordinate the sensor input from each of the sensing units with a rotating magnetic pulse generator geared to the linear motion of the pipe being manufactured. A purpose of this device is to actuate one or more spray cans at the linear and the circumferential position where a manufacturing flaw is detected either by the linear inspection unit or the rotary inspection unit. Application of such a testing device to on-site underground pipelines has not been demonstrated.
Another exterior pipe testing device has been disclosed in U.S. Pat. No. 4,439,730, in which pairs of north and south poles of magnets are held adjacent to the exterior wall of a pipe at uniformly spaced apart positions circumferentially around the pipe. The north and south poles are positioned between the north and south poles of longitudinally spaced apart circular magnets around the pipe. The circumferential spaced apart magnets are rotated at a high rate of speed so that orthogonically directed resultant magnetic field is produced on opposite sides of the pipe between the north and south pole of the rotating magnets. Pairs of flux detectors are interposed on opposite sides of the rotating magnet. The magnets are rotated at a sufficiently high rate of speed relative to the longitudinal motion of the pipe since the flux field interruptions in the same incremental area of the pipe. Again, complex circuitry is required in order to coordinate the sensor input from each of the sensing units because of the high rotational speed (320 revolutions per minute in the example set forth in '730) in order to keep track of the sampled signals from the two overlapping sensors and further, to coordinate them to a longitudinal position along the pipe. At a longitudinal travelling speed of 80 feet per minute as set forth in the example, the device must make four complete revolutions during every one foot of travel, which is consistent with the sensor field slightly over three inches long, so that 100% of the pipe surface can be covered.
Pipeline flaw detectors for use inside of existing pipelines have also provided rotary mechanisms for rotating sensing shoes helically through the pipeline as the detector is moved linearly therealong. One such device is disclosed in U.S. Pat. No. 3,238,448 which, upon detecting a flaw, actuates a strong electromagnet to magnetize the corresponding portion of the pipeline so that the position of the defect can be detected from aboveground with magnetic sensors. This device rotates two opposed search units in a single direction such that only very large flaws can be accurately detected and locating any such detected flaws is dependent upon a second careful searching action for the magnetized pipe section from above ground.
Another pipeline inspection apparatus is disclosed in U.S. Pat. No. 4,072,894 which produces a circumferentially directed magnetic flux field as flux leakage detection sensors are resiliently held against the pipe wall surface and helically moved through the pipe to pass transversely across any longitudinally extending anomalies in the pipe wall.
One of the most popular and currently the most widely used state-of-the-art internal magnetic flux gas pipe inspection devices comprises a pipeline pig which has sealing cups around the exterior perimeter to both center the apparatus and to drive it by differential gas pressure along the pipeline. A magnetic flux is generated by multiple circumferentially spaced magnets with north and south poles axially spaced apart and a magnetic flux sensor interposed therebetween. In operation, the pig travels linearly through the pipeline and sensory input data from each sensor is recorded as a function of distance of travel. When a defect, void, or other anomaly in the pipe is indicated by sensing an interruption of a smooth longitudinal magnetic flux, then such an anomaly is recorded on a graph as a function of time or distance. A major drawback of this device is that the longitudinal, or axially aligned, magnetic flux cannot always detect longitudinal voids or defects such as a uniform deterioration along a continuous welded seam of the pipeline. Resolution is determined by the size of the multiple sensor unit. A second set of circumferentially positioned magnetic flux generators and flux leakage sensors can be positioned at a small staggered distance with respect to the first set so that the space between the flux generator and sensor shoes is covered by the second set of sensors.
One of the regulations that both state and federal agencies have is a requirement that each length (joint) of pipe installed in a pipeline be documented as to the "grade" of steel used in the making of the joint of pipe. The records of many pipelines have been lost or poorly kept. The Federal Department of Transportation (DOT) has, as of 1997, given the pipeline owners five years to bring their records into compliance. Line pipe is identified by size, wall thickness and grades. Intelligent pigs, as described hereinbefore, presently measure thickness, joint length, geographic position and other physical parameters. Pipe grade is controlled by the steel mill which produces the pipe. It is confirmed by testing. The grade can be confirmed by pressure tests and tensile tests. Over the years, mill records for joints of pipe may be lost and/or undocumented joints may be placed in the pipeline. Should a pipeline contain one or more undocumented pipe joints, the DOT regulations require that the pipeline be operated at pressures assuming the pipe grade is 24,000 p.s.i. This would require that many pipelines lower their operating pressure to uneconomical levels. Many pipelines in the U.S. are operating in excess of the legal allowable pressures.
In order to "document" the grade of the pipe joints, two techniques can be employed. First, coupons may be cut from the line at various intervals. These coupons are then tested by pulling to yield so as to determine tensile strength. This method requires that the line must be removed from service. As such, this is a costly approach. Furthermore, this method can produce damage which may accelerate pipeline failure.
An alternative technique is to show that the pipe is of the grade the pipeline is rated at by a preponderous of evidence. To establish the grade of the pipeline, it is important to note that grades of pipe made at approximately the same time (year) have the same basic properties of: (1) chemical composition; (2) density (velocity of sound); (3) magnetic (eddy current field) and (4) hardness (Vickers B indentation). By measuring one or more of these properties in a documented joint of pipe in a line, other joints can be compared to this "standard". In this manner, each joint can be confirmed to be the same or different than the "standard" joints of pipe. This method allows for an intelligent inspection tool (i.e. the pig) to be designed to compare the grade of each joint of pipe. When coupled with the information from another tool, such as a Geopig, its location in the pipeline, its geodetic position, and the grade of each joint can be verified.
Presently, tests of density (speed of sound), and magnetism (conductivity) can be achieved with the pigs of the prior art, as described herein previously. A hardness test may be made with a MICRODUE (MIC 10). This established hardness tester operates according to the ultrasonic contact impedance method. This method enables quick and easy measurements by positioning the probe and reading off the value. This operational ease is achieved because Vickers diamond indent in the material's surface is electronically measured and instantly displayed as a hardness value without using the cumbersome optical evaluation of the microscope normally associated with Vickers hardness testing. The MIC 10 is a very easy instrument to use. It is a hardness tester that can be transported anywhere for testing components at any location. The small narrow probe can even enable one to make measurements at positions that are difficult to access, such as tooth flanks or roots of gears. It can be measured in any direction, e.g. in the horizontal or overhead position. In order for the MIC 10 probe to be properly used, it must remain relatively static relative to the item to be tested for a short time, i.e. 30 milliseconds. Once the reading is obtained, the data can be transmitted via an RS232C port to a master data memory located at a desired location.
It is an object of the present invention to prove a method and apparatus for the testing of the hardness of an interior surface of a pipeline.
It is another object of the present invention to prove a method and apparatus which allows an MIC 10 probe to momentarily remain static during the movement of a pig through the pipeline.
It is a further object of the present invention to prove a method and apparatus which facilitates the determination of the grade of the pipeline by a preponderance of evidence.
It is a further object of the present invention to prove a method and apparatus for the measurement of the hardness of a pipe which allows for the documentation of the grade of pipe joints.
It is still a further object of the present invention to prove a method and apparatus for the measurement of pipeline hardness which is easy to use, easy to install, easy to manufacture, and relatively inexpensive.
These and other objects and advantages of the present invention will become apparent from a reading of the attached specification and appended claims.